1. Field of the Invention
This invention relates to a method of manufacturing an electronic part comprising a plurality of single-layer plates laminated in succession, and an electronic part, and particularly to a method of manufacturing an electronic part suitable for forming an electrical conductor for effecting connection between adjacent ones of the single-layer plates, and an electronic part.
2. Related Background Art
There is known such an electronic part as forms a conductor portion extending through single-layer plates, and superposes these one upon another to thereby effect connection between the single-layer plates.
In the single-layer plates, there have heretofore been proposed and disclosed various manufacturing methods for forming a conductor portion for effecting the connection between layers. FIGS. 6A to 6D of the accompanying drawings are step illustrations showing the conventional manufacturing process of the single-layer plate of an electronic part.
In a single-layer plate constituting an electronic part, as shown in FIG. 6A, there are formed in advance a base member 1 formed of an insulating material having a predetermined thickness, and conductor film 2 and a lower conductor layer 3 formed on the opposite sides of the base member 1.
To form an upper wiring pattern 4 and a lower wiring pattern 5 (see FIG. 7C of the accompanying drawings) on the opposite sides of the single-layer plate of such a form, dry film 6 providing resist is first attached so as to cover the conductor film 2. After the dry film 6 has been attached, exposure and development are effected to thereby form an aperture 7 corresponding to the diameter of a conductor portion which will be described later. After the aperture 7 has been thus formed in the dry film 6, as shown in FIG. 6B, etching is effected on the conductor film 2 exposed on the bottom surface of the aperture 7 to thereby remove the exposed conductor film 2 from the aperture 7 and expose the base member 1.
After the base member 1 has been thus exposed on the bottom of the aperture 7 by the etching process, as shown in FIG. 6C, the dry film 6 is peeled off and also, an opening portion 8 corresponding to the diameter of the aperture 7 is formed by laser irradiation. After the opening portion 8 has been thus formed, as shown in FIG. 6D, electroless plating which is chemical plating is uniformly effected on the upper layer side and opening portion 8 of the base member 1 to thereby form an electroless plating layer 9.
After the electroless plating layer 9 has been formed, electroplating is effected with the electroless plating layer 9 as electric power supplying film (electrode) to thereby precipitate a metal 10 in the interior of the opening portion 8 and on the upper side of the conductor film 2. This state is shown in FIG. 7A of the accompanying drawings. As shown in FIG. 7B of the accompanying drawings, the interior of the opening portion 8 is then filled with the metal 10 by electroplating whereafter as shown in FIG. 7C, patterning is effected on the conductor film 2 and the lower conductor layer 3 by a subtractive method, to thereby form the upper wiring pattern 4 and the lower wiring pattern 5 and also, form a conductor portion 11 in the opening portion 8.
Now, in the foregoing conventional example, an electroless plating layer has been used to contrive an improvement in the close contact between the base member and the conductor portion 10 (see, for example, Japanese Patent Application Laid-open No. H11-343593), but there is also known a method of applying other processing in place of the electroless plating layer (see, for example, Japanese Patent Application Laid-open No. 2001-217553).
However, the use of the above-described electroless plating (and other method replacing the electroless plating) has posed such a problem as shown below.
That is, if as shown in FIG. 7B, an attempt is made to effect electroplating to thereby fill the opening portion 8 with the metal 10 after the electroless plating layer has been formed, there has been the problem that a plating layer is thickly formed on the whole of one side of the base member and as the result, when as shown in FIG. 7C, wiring patterns are to be formed by etching, the cross sections of the wiring patterns become trapezoid, and dimensional accuracy is reduced and wiring patterns of a narrow width cannot be formed.
Also, when the electroless plating layer 9 is formed and electroplating is effected with this as an electrode, fresh plating liquid is more applied to the surface of the electroless plating layer 9 than to the inside of the aperture. Therefore, the growth of the electroplating layer on this surface is promoted and as the result, there has been the possibility that before the opening portion 8 is filled with the metal material, the opening portion 8 is closed (by the electroplating layer) and a so-called void forms in the interior of the conductor portion 3.
Also, there has been the possibility that a similar problem arises when the electroless plating is not used, but other ante-processing is effected.
Now, when electroless plating is used, a metal catalyst is used to cause plating to adhere also to other portion (insulator portion) than a conductor. However, if this metal catalyst is residual on the surface of a wiring layer, there has been the possibility that an insulation resistance value is reduced or an obstruction such as the short-circuiting of the wiring pattern is caused. In the electronic parts in recent years, a narrower pitch is advanced and the possibility of the above-noted obstruction has become higher.